linux-kernel - Re: [PATCH v2 2/4] dmaengine: Add STM32 DMA driver

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Date:	Wed, 14 Oct 2015 17:26:04 +0200
From:	"M'boumba Cedric Madianga" <cedric.madianga@...il.com>
To:	Daniel Thompson <daniel.thompson@...aro.org>
Cc:	Maxime Coquelin <mcoquelin.stm32@...il.com>, robh+dt@...nel.org,
	pawel.moll@....com, Mark Rutland <mark.rutland@....com>,
	ijc+devicetree@...lion.org.uk, Kumar Gala <galak@...eaurora.org>,
	linux@....linux.org.uk, Vinod Koul <vinod.koul@...el.com>,
	linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, dmaengine@...r.kernel.org
Subject: Re: [PATCH v2 2/4] dmaengine: Add STM32 DMA driver

2015-10-14 16:24 GMT+02:00 Daniel Thompson <daniel.thompson@...aro.org>:
>
> Hmnnn...
>
> The dmaengine framework will WARN_ONCE() if an dmaengine is removed whilst
> it is active and also works hard to ensure dmaengine modules are not removed
> whilst there are active drivers using the framework.
>
> How do we get into this function whilst there is still an active DMA
> channels?

For example, when a user try "rmmod stm32-dma" in uart console.
It will enter in stm32_dma_remove while there is potentially still active DMA.

>
>
>> But even with this improvement, I think I have to disable the clock here.
>
>
> As above, I think the dmaengine framework work to protect you from this sort
> problem. However even if I am wrong about that then unconditionally calling
> clk_disable_unprepare() can not be used to reliably manage the clocks. You
> don't know what the counts are!

Ok got it. Thanks for the clarification.

Cedric
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